The present invention relates to a method for manufacturing a fiber type coupler for splitting or merging a propagated light in an optical fiber, and more particularly to a method for manufacturing the fiber type coupler including a step of fusing and extending a plurality of optical fibers.
2. Related Background Art
The fiber type coupler has a function to split and couple single wavelength lights or split and merge multi-wavelength lights. The manufacturing method thereof includes a fuse extension method in which fibers are fused and extended, and a grind method in which two optical fibers having sides thereof ground are faced each other.
FIG. 1 is a flow chart which shows a related background art of fiber type coupler manufacturing method (fuse and extend method). (Electronics Letters, 15th Mar. 1984, Vol. 20, No. 6, PP. 230-232) A fiber type coupler which uses a single mode fiber is now explained.
Coatings of two optical fibers are partially removed and the optical fibers are contacted to each other (step 101). Then the contracted areas are fused parallelly by heating them with a burner and then the optical fibers are extended along the optical axis (step 102). In this case, a light applied to one end of the optical fiber is measured at the other end to detect a light split ratio (step 103). If a predetermined split ratio is obtained, the extension of the optical fiber is stopped and a coupler member is formed (step 104). Then, the coupler member is fixed and bonded to a protective member to form the fiber type coupler (step 105).
In other related background art method, two optical fibers are not fused and extended but twisted and heated and extended ("A Discussion on A Manufacturing Method of a Biconical Tapered Distributor", 1984 National Conference of Light-Electromagnetic Wave Section of the Institute of Electronics and Communication Engineers of Japan).
The related background art fiber type coupler is fixed to the protective material by the bonding material. The coupler whose diameter has been reduced by the extension has a diameter of less than 20 .mu.m which is almost one tenth of the diameter before the extension.
As a result, the tensile strength at the coupler is remarkably reduced, and it may be broken in the heat cycle.
Thus, the related background art fiber type coupler exhibits a low reliability is an environment where the heat cycle is applied.